EAR 834P needing repair

[Paul Ebert]

I have an EAR 834P that has developed distortion on the left channel. It only occurs on certain relatively high frequency sounds. I've replaced the tubes but that didn't help.

Anyone able (and willing) to help me fix it? If anyone had a schematic they'd be willing to share, that would be a good start.

Based on my experiences (not with EAR, but with commercial audio components in general), I'm not very enthused about sending it to a dealer for repair. If I cannot fix it, I'll probably build a solid state phono preamp (maybe the PhonoClone).

Thanks!

 

[HollowState]

Originally posted by Paul Ebert
If I cannot fix it, I'll probably build a solid state phono preamp.

Egad man....that's heresy!

 

[analog_sa]

The circuit is well known and extremely simple. Shoot me a PM and i'll email it to you. It may be a defective passive component or even a bad socket.

 

[analog_sa]

Or much better have a look here

 

[SY]

Hmmm, no schematic at that link. Not much real info, either. Is this the cascode pre?

 

[korneluk]

The EAR834P schematic can be found here:

http://bbs.hifidiy.net/viewthread.php?tid=92192&extra=page=1&filter=type&typeid=10&page=2

and here:

http://www.audiocircle.com/gallery/displayimage.php?album=546&pos=0

Enjoy,

-- josé k.

 

[SY]

Jose, thanks. Interesting.

 

[Paul Ebert]

Thanks for the help. I think I'll, at least, take a stab at fixing it. It doesn't look too complicated.

Any suggestions on how to start? I suppose I could start making Thorsten's mods and see if I end up replacing the faulty component.

 

[SY]

It's generally a bad idea to start modifying something that isn't working. Fix the problem first, then you can start spending money on random fashion componentry.

I'd start by measuring the plate and cathode voltages of each stage and indicating them on the schematic. Compare them between channels.

 

[Paul Ebert]

Yeah, I can see what you're saying. I'll give that a try.

Thanks.

 

[analog_sa]

If it sounds like distortion i would suspect bad solder joint/ socket before anything else. Leaking caps would be next on my list.

 

[SY]

Could be. But the description sounded like an overload situation which could be due to an operating point shift:

It only occurs on certain relatively high frequency sounds.

 

[KaDe]

As I recall the amp runs into HF-oscilation with the wrong tube in V3 position.
I would go for a low transconductance type like ECC82/12AU7 here.
You may also need to try different manufacturers, there is a large spread of various constructions around the ECC82 .

 

[bip]

My EAR 834P phono preamp has developed a loud hum in the left speaker. My question is: should I replace the 3 tubes or is this possibly indicative of a problem other than tube malfunction?
Thanks

 

[Steve Morley]

A broken wire or bad solder joint between the jacks and the board maybe? Does yours have the built in SUTs? Maybe the MM MC switch is dirty.

Every tube is shared between both channels. It's not unknown for the two haves to age differently but not likely that only one side would go real bad.

Remove and reinstall all of the tubes 3 or 4 times. Might be a dirty connection between tubes pins and socket.

Steve